Compensating device for thermo-couples



C. B. THWING.

COMPENS-ATING DEVICE FOR THERMO COUPLES. APPL|cA1 1oN HLED Nov. 3o, ma.

UNITED STAT-Es PATENT OFFICE.

CHARLES IB. TI-IWING", OF PHILADELPHIA, PENNSYLVANIA, rASSIGrNOR T0 THWING INSTRUMENT COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

COMPENSATING DEVICE FOR THERMO-COUPLES. i'

To all whom t may concern.'

Be it known that I, CHARLES B. THWING, a citizen of the United States, residing vin Philadelphia, Pennsylvania, have invented Compensating Devices for Thermo-Couples, of which the following is a specification.

As' is understood by those skilled in the thermo-electric art, there is an error in the indications of a galvanometer connected to a thermo-couple, by reason of the variations of temperature occurring at the cold end of the latter, so that it is necessary, in order that the readings of the galvanometer shall be due solely' to variations of temperatureof the hot end of the thermo-couple, to provide some device whereby the temperature variations of the cold end shall be compensated for or corrected.

One object of my invention therefore, is to provide a compensating device for instruments of the class above indicated which in addition to satisfactorily performing its required functions, shall be inexpensive and of such a nature as will permit of its being installed at a distance from the thermo-couple or couples with which it is designed to operate ;-usually at a point adjacent the lindicating galvanometer.

'These objects and other advantageous ends I attain as hereinafter set forth, reference being had to the accompanying-drawings, in which: g

Figure 1 is a diagrammatic view illustrating one form of my invention; and

Fig. 2 is a view similar to Fig. 1, showing a modification of the invention.

In Fig, 1 of the above drawings 1, 2 and 3 represent thermo-couples having their hot ends within tubes 4 which may be mounted within a stack, kiln, furnace or other structure or apparatus whose temperature it is desired to record or indicate. In the present instance, the three thermo-couples are designed for use in three different parts of a furnace and each of the containing tubes 4 has connected to or associated with it a junction box 5 into which the cold ends of said thermo-couples project. In addition, each thermo-couple has connected to its terminals a pair of conductors 6 and 7 constitutingextensions, and as they are made of the same metals as the elements of their respectivev thermo-couples` they are usually of reduced cross section. All of these extensions project Specification of Letters Patent. Patented June 22, 1920 Application filed November 30, 1918.

Serial No. 264,873.

' into and terminate within a common junc- ,materials as those of said thermo-couples 1,2 and 3 constituting thermo-couple extensions, which are run into and terminate in a lcavity in the ground indicated at 23, constituting a cold end well. From said cold end terminals two copper or relatively inexpensive metal conductors 24 and 25 lead to the adjustable blade 26 of the switch 15 and to the secondterminal of the indicating instrument 18 respectively.

The cold end of the auxiliary thermocouple is thus maintained at a substantially constant temperature by being placed in the c old end well 23, and the latter may be situated at any convenient point, preferably near the indicator 18. The electromotive force of this thermo-couple is thus dependent solely on the variations of temperature occurring in the common junction box 8 which likewise affect the cold ends of the thermo-couples 1, 2 and 3 and as a result the auxiliary thermo-couple exactly counteracts or compensates for the variations in the electromotive force of the thermocouples 1, 2 and 3, being connected in series with the indicator 18 and with any one of said. thermo-couples according to the position of the switch blade 26 relatively to the contacts 12, 13 or 14. a

In some cases it may be advantageous to provide the auxiliary thermo-couple and its cold end well arranged as above described when but a single main thermo-couple is employed. The hot end of the auxiliary thermo-couple 19 in this case is placed in the junction box 5 and as before it has extensions 21 and 22 which terminate in the cold end well 23. A switch 15a is connected between one of the cold end terminals and one terminal of the main thermo-couple so as to allow of the current being out off from connected respectively to the second thermocouple extension of each pair; a cold well;

an auxiliary thermo-couple having its hot end in the common junction box and its cold end in the cold well; with conductors respectively connecting the cold end terminals of the auxiliary thermo-couple with another Contact of the switch and with the second terminal of the indicator.

2. The combination of a series of thermocouples each having extensions; a common junction box receiving said extensions; an indicator; conductors connecting certain of the thermo-couple extensions with one terminal of the indicator; a cold well; an auxiliary thermo-couple having its hot end in the common junction box and its cold end in the cold well; with means for connecting at will said auxiliary thermo-couple inseries between the second terminal of the indicator and any of the remaining thermocouple extensions.

3. The combination of a series of thermocouples, each having extensions; la common junction box entered by said extensions; an indicator; a multiple switch; conductors connecting certain of the thermo-couple extensions with one terminal of the indicator; other conductors connecting the remaining thermo-couple extensions to the switch; a cold well; an auxiliary thermo-couple having its hot end in the common junction box and its cold end in the cold well; with conductors connegcting said auxiliary thermocouple with the switch and with the second terminal of the indicaton 4. The combination of a plurality of thermo-couples; extensions for each of said thermo-couples; a junction box entered by said extensions; an indicatingv instrument connected to certain of said extensions; a cold well relatively distant from the thermocouples; an auxiliary thermo-couple having its hot end in the common junction box and its cold end in the vcold well; and means including a switch for connecting the auxiliary thermo-couple in series with the indicator and any of the other thermo-couples at will. f 1

5. The combination of a main thermocouple; extensions y"for said thermo-couple; a junction box for said extensions; an indicating instrument; a base metal conductor connecting one of the indicator terminals to one of the thermo-couple extensions in said junction box; a cold well relatively distant from the thermo-couple; an auxiliary thermo-couple having its hot end in the junction box and its cold endin the cold well; with means for connecting said auxiliary thermo-couple between the second extension of the main thermo-couple and the second terminal of the indicator.

In witness whereof I afiix my signature.

CHARLES B. THWING. 

